src: remove public API for option variables

PR-URL: https://github.com/nodejs/node/pull/23069


Reviewed-By: Gus Caplan <me@gus.host>
Reviewed-By: Joyee Cheung <joyeec9h3@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Shingo Inoue <leko.noor@gmail.com>
Reviewed-By: Refael Ackermann <refack@gmail.com>